Marine tankers



Feb. 5, 1963 J. F. LEATHARD MARINE TANKERS 4 Sheets-Sheet 1 Filed April 1, 1958 mm mw NN NM, NN NM,

Feb. 5, 1963 J. F. LEATHARD 3,076,423

MARINE mms Filed April 1, 1958 4 Sheets-Sheet 3 a R7 I l lng/int @uw fw ttorneys Feb 5 1963 J. F. LEA-THARD 3,076,423"

MARINE TANKFRS Filed April l, 1 958 4 Sheets-Sheet 4 A F um A ttorneyg ilnited States Patent 3,d76,423 MARlNE TANKERS .lohn Frederick Leathard, Worting, near Basingstoke, England, assigner to Wm. Cory di Son Limited, London,

England Filed Apr. l, 1953, Ser. No. 725,675 Claims priority, application Great Britain Apr. 5, 1957 17 Claims. (Cl. 11d- 74) This invention relates to water-borne tankers, particularly ocean-going tankers, for the transport in liquid form at low temperature and approximately atmospheric pressure, of substances which are normally in a gaseous state. The gas which cornes mainly into question is methane, but the references herein to methane are, wherever the context allows, to be read as references also to like gases which it may be desirable to transport in the liquid state.

The present invention is concerned mainly with large tankers, for example of the order of 16,060 deadweight tons, having a number of large insulated methane tanks each of which extends across practically the Whole breadth of the Vessel. The large size of the tanks demands that they be properly supported in the ship so that they do not shift in rough seas, but at the same time the supporting means must be so constructed as to allow for thermal expansion and contraction of the tanks both radially and axially. This arises from the comparatively Wide emperature range to which they are subjected, i.e. from normal temperature down to that of liquid methane (minus 266 E), and also from the metal out of which the tanks are constructed. Aluminium-magnesium alloy, for example, is very satisfactory for this purpose, as its mechanical properties are not adversely aiiected at the temperature of liquid methane, and it can also be Welded without diculty.

According to the present invention, there is provided, in a marine tanker for the bulk transport in the liquid state at low temperature of methane (or like ordinarilygaseous substance), one or more cargo tanks each of rwhich rests on supports which allow lateral expansion and contraction of the tank but is constrained against lateral bodily displacement by at least one connection, such as a spigot-type connection, provided between the tank and the ships structure at the tank bottom center or the tank top center or both. p

Each tank may be constructed with integral spigots at both its top center and its bottom center, which spigots are rereived in cooperating seatings of the ships structure. The spigot connections, being at the tank center, do not prevent lateral thermal expansion and contraction of the tank.

in the preferred arrangement, each tank rests on a plurality of rollers arranged with their axes normal to a plu- -ralty of lines radiating from the tank vertical axis. These rollers serve to take .the downward load of the tank and its contents. Upward loads, due, for example, to pitching of the ship may be taken by anchoring chains provided between the ships structure and the tank.

ln order that the invention may be thoroughly understood, a speciiic methane tanker in accordance therewith will now be described in some detail, by way of example, and with reference to the accompanying diagrammatic drawings in which:

FlGURE l shows in elevation a marine tanker for the transport o methane,

FlGUiE 2 is a plan showing the arrangement of the methane tanks in the holds,

FIGURE 3 is a cross-sectional elevation of one of the main cargo tanks and its installation,

FlGURE 4 is a plan of the tank bottom,

FIGURE 5 is a sectional elevation of a ydetail of the tank bottom,

ice

PEGURE 6 is a cross-section on the line 6-6 of FIG- URE 5,

FIGURE 7 is a detailed view to a larger scale of a tank-supporting anti-friction roller of FIGURE 5 showing its mounting,

FlGURE 8 is a sectional elevation of a detail of the tank top, and

FIGURE 9 is an alternative arrangement to that shown in FIGURE 8.

ReferrinfI firstly to FlGURES 1 and 2, the cargocarrying section of the tanker hull liti is divided into six separate main hold compartments ll to lo by a series of transverse bulkheads i7'. Disposed individually in the hold compartments l1 yto lo, in a closely-spaced roiw along the fore-and-ait center line of the vessel are six main cargo tanks ld to 23. These main tanks are, for the most part, substantially cylindrical in form with their principal axes vertical, and in general they extend at their widest parts for substantially the whole width of the vessel although tanks i? and 23 are somewhat less in diameter than tanks 2d, 2l and 22, and the most forward tank l@ is a good deal less in diameter.

The vessel is of turret construction, that is to say it has a main deck at the level 24 and a narrower turret deck above at the level Z5. Each of lthe main tanks i8 to 23 extends up through the main deck at level 24, and, with the exception of the tank 2d, the portions of the tanks tha-t protrude above the main deck are as large in diameter as can be conveniently accommodated within the turret structure 25. To this end, tanks i9, 2l, 22 and 23 have stepped-in upper portions 2S, 2'?, 3d and 3l but the forward tank iii, being already relatively narrow, does not need to be stepped-in. Each of the six tanks terminates at its upper end in a narrow neck 27 surmounted by a pump motor housing 32. ln the case of the live tanks 1S, i9, 2l, 22 and 23 the narrow tank neck 27 reaches up through the turret deck at level 25' and the housing 32 is situated on said deck, but the tank 2th, for reasons which need not be discussed here, is not as high as the other five, having its neck 27 terminating only just above the main deck level 24 and its pump motor housing 32 disposed on the main deck Within the turret structure.

Owing to the circular plan form of the main tanks lh to 23, there is an appreciable space below decks between one tank and the next at opposite sides of the vessel, and in the case of tanks 19 to Z3 these spaces between are utilised by disposing in them eight additional wing tanks S3 of much smaller capacity. The wing tanks 33 are all cylindrical with their principal axes upright, and are located wholly below the main deck level 24. As will be seen in FIGURE 2, the arrangement oi bulkheads between the main tanks 19 to 23 is such that each wing tank 33 has its own individual water-tight hold compartment 34, each oi the bulkheads i7 branching, as it were, into two diverging bulkheads 3s" to embrace a wing tank as it approaches each side of the huil.

Referring now to FIGURE 3, this shows the construction of one of the main cargo tanks and its disposition in its hold compartment. To give an idea of the size, in a ship of approximately 16,600 tons deadweight the largest of these tanks would have a capacity of the order of 280,000 cubic feet, and each of the Wing tanks would have a capacity of about 9,000 cubic feet. As will hereinafter be described in detail, the tank bottom rests on rollers so as to enable lateral expansion and contraction to take place, and is anchored against lateral shitting bodily by means of spigots at the top and bottom of the tank.

As seen in FIGURES 3 and 4, the tank bottom 9d is of welded plate construction stitened by internal circumferential and radial mem-bers. The principal radial members 91 are spaced at equal angles of approximately 18 and run from the centre spigot 92 to the inside of the tank corner plating. Stealer stiffeners 93 are also provided between the principal radial stifeners 91, extending from the periphery of the tank bottom part way in toward the center spigot 92. The tank support points occur radially along the principal stiifeners 91, and at each point of support there is a circumferential tripping plate 94 intersecting the principal stifeners 91 and stealers 93.

The lower corner of the tank around the margin of the tank bottom is of cellular construction, and apertured radial corner brackets 95 follow the lines of the principal bottom stiffeners 91. This bottom corner of the tank follows the line of the ships inner bottom at the bilge, the shape being kept constant all around the circumference of the tank. It may be here remarked that all the internal corners of the tank are mitred, as will be seen, to avoid too abrupt angular discontinuities of the tank surface (the same end could alternatively be achieved by rounding the corners).

The sides of the tank, which are vertical, have vertical stiffeners 97, and equally spaced throughout the depth of the tank are provided circumferential stringers 98 which have scantlings determined by consideration of the bending moments in the tank at the different depths of the liquid. Tripping brackets 99 are arranged between the vertical stiffeners 97 and the circumferential stringers 9S and the stitfeners 97 are also adequately bracketed to the members of the tank bottom and tank top.

The top of the tank is substantially parallel to the deck and turret top, as seen. The general principle of construction of the tank top is similar to that of the tank bottom, with stifeners and stealers radiating from the top center spigot 101 and intersected by circumferential tripping plates 102. The step between the full diameter and turret sections of the tank is provided by the inclusion of vertical members 103 arranged to piek up, at top and bottom, the radial stiifeners 104 in the top of the turret section and in the top of the full diameter part of the tank. One or more circumferential stiffeners 165 can be provided around the turret section of the tank, with associated bracketing if necessary, as in the case of the sides of the main part of the tank.

A practical consideration in tank design is the possibility of reducing scantlings in the fore-and-aft direction, due to the fact that the vessels pitching angle will be less than the rolling angle so that the design criteria in that direction are not so stringent. The level of thermal stresses, due to temperature differentials between various parts of the tank, are reduced to a minimum by eliminating, as far as possible, too abrupt discontinuities in the tank structure as previously mentioned.

The tank is entirely surrounded by insulation; granular insulating material 106 is provided between the tank bottom and the bottom of the ships hold compartment housing the tank, while the sides and top of the tank are insulated by means of fiberglass mat 107, or its equivalent. As will be seen, clearance space is provided between the top of the tank and the ships structure to allow for expansion and contraction of the tank.

As previously mentioned, the supporting members under the tank take the form of a number of rollers. These rollers 108 are located at intervals along a plurality of lines extending radially outwards from the aXis of the tank, that is to say the lines of the principal stiifeners of the tank bottom, on stools 109 fixed to the hull of the ship.

The stools 169 are of aluminium and have base plates secured by bolting to steel ground bars or seatings 12,9 of angle section welded on to the ships inner bottom 13d, pads 131 of a tough load-bearing heatand electricalinsulating material such as TufnoL being interposed 4 between the base plates of the stools 109 and the seatings 129.

The roller axes are set normal to the aforesaid radial lines so that radial movement of the tank bottom due to expansion and contraction is not impeded in any way, andeach roller is relative-ly short being substantially the same `dimension in diameter as it is in length. The rollers are preferably made of a resin-bonded laminate material which is capable of bearing the load and at the same time lacts Ias a thermal barrier between the tank and the ships structure. A suitable material is that sold under the trademark Permali by Permali Ltd. As seen in FIG- URES 5 and 7, the rollers 108 have spindles journalled in holes in upstanding lugs 110 on the stools 109, which holes are elongated horizontally to permit the maximum movement of the roller which will occur during expansion and contraction of the tank.

The weight of the -tank and its contents will normally keep Athe tank bottom in contact with the rollers, but upward movement of the tank may be possib-le as the vessel heaves in heavy seas or if the cofferdam spaces are ooded under certain emergency arrangements. Such movement is prevented by anchoring chains 150 which connect the bottom of the tank to the part of the hull beneath it. These chains are arranged close to the roller stools and are disposed to make as small an angle as possible with the vertical so as to allow radial movement of the tank due to thermal expansion and contraction without tending to distort the tank. Chains are chosen for this purpose `as 4the contact surface between each link is small and does not, therefore, provide a significant heat path from the ship structure to the tank or allow local col-d spots to occur in the ships structure.

In order that bodily lateral shifting of the tank may be prevented, the central spigots 101, 92 at the upper and lower ends of the tank are loca-ted in upper and lower seatings 111 and 112 (FIGURES 5 and 8) integral with the ships structure. The bottom spigot 92, which is of hollow cylindrical form, is housed in a steel ring 113 rigidly attached tothe bottom structure of the ship (FIG- URES 5 and 6). An annular space is provided between the spigot 92 and the ring 113, and in this annular space -are located two concentric channel-section rings 114, 115 made of material such as that sold under the trademark Permali, each ring actually comprising a number of separated segments with gaps between. Between these two concentric rings in the channels thereof are arranged a number of flexible rubber or plastic cushions 118, which are contained between segmental channel liner pieces 116, 117 of extruded aluminium and are filled with an hydraulic liquid which does not freeze at moderately low temperatures. A suitable liquid is Lockheed No. 33 brake fluid. The function of these cushions is to hold the spigot 92 firmly in position while at the same time allowing for radial expansion and contraction of the spigot. To act as end restraints for the individual cushions, and limit their circumferential expansion, Permali webs 119 are fitted at the gaps in the rings 114, 115.

Hydraulic uid is supplied to each cushion 118 through branch pipes connected to a circular main (not shown) located in ythe space surrounding the steel ring support. The required pressure in the main is obtained by an hydraulic booster in association with a pump. When the ship arrives in port to be unloaded, the pressure in the main is lowered so tha-t, on discharge of the methane cargo, thermal expansion of the spigot 92 can take place against the elasticity of the cushions 118. After the discharge of methane has been completed and the ship starts on her ballast voyage, the spigot ceases to expand and more liquid is pumped into the cushions and retained at -a pre-determined pressure so that lateral movement of the spigot due to the motion of the ship is prevented. On arrival of the ship at the loading port, the tank is lilled with methane 'and contraction of the spigot will take place. Additional hydraulic fluid is therefore pumped into the cushions and kept at the required pressure so that later-al movement of the tank will again be prevented whilst at sea. The fact that the inner ring 115 of Permali material is in segmental form allows this ring to follow the thermal movement of the spigot.

The interior of the bottom spigot 92 forms a sump for the tank, and the discharge ot methane from the tank is preferably eiiected by a vertical turbine pump with a. suction Ipipe, which extends down into the bottom spigot.

The spigot lill on the top o-f the tank (FIGURE 8) is generally of the :same design as the bottom spigot and is similarly housed in a steel ring support 120 having concentric rings 121, 122 of Permali material, aluminium liner pieces 123, 124, and a number of hydraulic cushions 125. The inner ring 122 of Permali material is not secured to the spigot 1to1 -as vertical thermal movement has to be allowed for as well as lateral movement. The outer ring 121 of Permali material is arranged in the form of a channel with wide flanges 126 and lthis supports the inner ring which is in segmental form. The outer ring is retained by lugs 127.

The interior of the top spigot 101 lactually aiords the narrow tank neck 27 previously mentioned in connection with FGURE l. The tank is ordinarily iilled to alevel up in this neck and its upper part above the liquid provides an evaporation chamber for the methane. lt also serves as a seating for the methane discharge pump and associated piping. The top of the spigot is fitted with 'a removable gas-tight and liquid-tight cover 128 to allow access into the tank when required.

FIGURE 9 shows an alternative seating lfor the top spigot itil in which the hydraulic cushions are omitted. In this arrangement there are concentric Permali rings 132, 133, one retained on the steel ring 120 of the ships structure by lugs 127 and the other retained on the spigot 101 by lugs 13d. The two rings 132, 133 have mating conical bearing surfaces at 135; if the cone angles are properly chosen, with regard to the relationship between vertical expansion of the tank and diametrical expansion o the spigot, the bearing surfaces will rem-ain in close contact when thermal movement of the tank occurs.

Each of the small wing tanks 33 of the vessel is of generally cylindrical form with a ilat bottom and a conical top, and the principle of construction and mounting of these tanks in the ship is similar to that already described for the main tanks. All the cargo tanks are fabricated throughout in welded aluminium alloy.

By means of the supporting system for the tank described above, the tank is held iirmly in position in the hull of the ship but is free to expand and contract as a result of changes in the temperature of the tank.

Although the tanker arrangement speciiically described herein is designed with a special view to the accommodation of liquid methane cargo tanks, it will be appreciated that the nature of the tanks and their installation is such that it is not necessary that a vessel for use as a methane carrier should be newly built for this sole purpose. rl`hus, it is possible to adapt an existing oil tanker to methane carriage by the installation in it of tanks according to the invention.

I claim:

l. In a marine tanker for the bulk transport in the liquid state lat low temperature of ordinarily-gaseous substance, the provision of at least one insulated cargo tank which rests on supports which allow lateral expansion and contraction of the tank but is constrained against lateral bodily displacement by a circular spigot-andsocket type connection between the tank and the ships structural steel at the tank bottom center. l

2. A tanker as claimed in claim l, wherein the tank is constructed with integral spigots at both its top center and its bottom center, which spigots are received in cooperating seatings of the ships structural steel.

3. A tanker as claimed in claim l, wherein the tank 6 rests on a plurality of rollers arranged with their axes normal to a plurality of lines radiating from the tank vertical axis.

4. A tanker as claimed in claim-3, wherein anchoring chains are provided between the ships structure and the tank to prevent upward `displacement of the tank in the ship.

5. A tanker as claimed in claim 4, wherein the rollers are composed of a load-bearing material having heatinsulating properties.

6. In a steel-hulled marine tanker for the bulk transport in the liquid state at low temperature of ordinarilygaseous substance, the provision in combination of at least one insulated cargo tank having a circular spigotand-socket type connection between the tank and the ships steel hull structure at the tank bottom center whereby the tank is constrained against lateral bodily displacernent, a plurality of rollers on which the tank rests such rollers being of a load-bearing material having heatinsulating properties and being arranged with their axes normal to a plurality of lines radiating from the tank vertical axis to allow lateral expansion and contraction of the tank to take place, anchoring chains between the ships lhull structure and the tank to prevent upward displacement of the tank in the ship, aluminum stools on which said rollers are mounted, steel seatings on the ships inner bottom to which said stools are secured, and pads of load-bearing heatand electrical-insulating material interposed between the stools and the steel seatings.

7. In a marine tanker for the bulk transport of liquetied `gas the combination of, a ships hull structure, a ships deck structure, at least one heavily-insulated cargo tank in the hull below the deck structure, a tank bottom spigot seating integral with the hull bottoni, a tank top spigot seating integral with the deck structure, an integral spigot on the tank at its bottom center which bot-tom spigot is received in the bottom seating, and a second integral spigot on the tank at its top center which top spigot is received in the top seating, and wherein at least one of the spigot seatings comprises hollow flexible pressure-iiuid-lled cushion members around the spigot between it and the ships structure, whereby longitudinal and later-al restraint may be provided when thermal movement of the spigot is not occurring, and thermal movement is permitted when the restraint is relaxed.

8. In a marine tanker for the bulk transport of liqueed gas the combination of, a ships hull structure, -a ships deck structure, at least one heavily-insulated cargo tank in the hull below the deck structure, a tank bottom spigot seating integral with the hull bottom, a tank top spigot seating integral with the deck structure, an integral spigot on the tank at its bottom center which bottom spigot is received in the bottom seating, and a second integral spigot on the tank at its top center which top spigot is received in the top seating, and wherein the seating for the top spigot comprises a seating ring member on .the ships structure surrounding the spigot, the spigot itself being or" cylindrical form, and two concentric rings of load-bearing heat-insulating material in the annular space between the spigot and the seating ring, one insulating .ring being in engagement with and constrained against axial movement with respect to the seating ring `and the other insulating ring similarly engaging and being constrained with respect to the spigot, and the two insulating rings having mutually-engaging relatively-sliding coned bearing surfaces the cone angle being so chosen having regard to the relationship between vertical expansion of the tank and radial expansion of the spigot that the bearing surfaces remain in contact during thermal movement of the tank.

9. In a marine tanker for the bulk transport of liqueiied gas, the combination of, a ships hull, a ships deck structure, .at least one heavily-insulated cargo tank dis- Iposed in the hull below the deck structure with its upright axis intersecting the :Eore-and-aft center line of the ship, a tank bottom spigot seating integral with the hull bottom and a tank top spigot seating integral with the deck structure said spigot seatings having a common axis coincident with the upright axis of the tank, an integral spigot on the tank at its bottom center which bottom spigot is received in the bottom spigot seating, and a second integral spigot on the tank at its top center which top spigot is received in the top seating and is capable of axial movement relative to said top seating upon axial thermal movement of the tank, and wherein at least the bottom spigot seating comprises hollow, flexible pressure-fluid-tilled cushion members around the spigot between it and the ships structure, and pressure Huid-line connections to said cushion members, whereby the amount of pressure lluid in the cushion members can be varied to provide longitudinal and lateral restraint when thermal movement of the spigot is not occurring, and to relax this restraint while thermal movement takes place.

10. A tanker as claimed in claim 7, wherein at least the bottom spigot seating comprises a seating ring member on the ships structure surrounding the spigot, the spigot being itself of cylindrical form, two concentric rings of load-bearing heatinsulating material in the annular space between the spigot and the seating ring, one insulating ring engaging the spigot and the other the seating, and separate metal liners for the two insulating rings between which liners the pressure-fluid cushions are disposed.

11. 1n a marine tanker for the bulk transport of liquefied gas the combination of, a ships hull structure, a ships deck structure, at least one heavily-insulated cargo tank in the hull below the deck structure, a tank bottom spigot seating integral with the hull bottom, a tank top spigot seating integral with the deck structure, an integral spigot on the tank at its bottom center which bottom spigot is received in the bottom seating, and a second integral spigot on the tank at its top center which top spigot is received in the top seating.

12. In a marine tanker for .the bulk transport of liqueed gas, .the combination of, a ships steel hull, at least one insulated cargo tank in the hull, a tank bottom steel spigot-seating integral with the hull bottom steel, and an integral spigot on the tank at its bottom center which spigot is received in said bottom spigot-seating to hold the tank against bodily lateral movements.

13. A tanker as claimed in claim 12, further compressing a deck structure, a tank top spigot seating integral with the deck structure, and an integral spigot on the tank at its top center which spigot is received in said top spigot seating.

14. In a marine tanker for the bulk transport of liquetied gas, .the combination of, a ships hull, a ships deck structure, at least one heavily-insulated cargo tank disposed in the hull below the deck structure with its upright axis intersecting the fore-and-aft centre line of the ship, .a tank bottom spigot seating integral with the hull bottom and a tank top spigot seating integral with the deck structure said spigot seatings having a common axis coincident with the upright axis of the tank, an integral spigot on the tank at its bottom centre which bottom spigot is received in the bottom spigot seating, and a second integral spigot on the tank at its top centre which top spigot is received in the top seating and is capable of axial movement relative to said top seating upon axial thermal movement of the tank.

l5. A tanker as claimed in claim 8, wherein at least the insulating ring engaging the spigot is of segmental construction with gaps between the segments to allow for radial thermal expansion and contraction of the spigot.

16. A tanker as claimed in claim 1l, wherein the bottom spigot has a hollow interior which is in communication with the tank interior and provides a drain sump for the tank from which a tank discharging pump draws.

17. A tanker as claimed in claim 11, wherein the top spigot has a hollow interior which is in communication with the tank interior and forms a neck for the tank into which the liquid content ordinarily rises, the upper part of Vsaid neck affording a collecting space for gaseous methane 4boilingoff in the tank.

References Cited in the tile of this patent UNITED STATES PATENTS 1,085,086 lack Jan. 20, 1914 1,866,517 Heylandt July 5, 1932 1,979,221 Dana Oct. 30, 1934 2,520,883 Kornemann et al Aug. 29, 1950 2,600,015 McLaughlin June 10, 1952 2,729,357 Nason et al Jan. 3, 1956 2,798,364 Morrison July 9, 1957 2,799,425 Werker July 16, 1957 2,810,265 Beckwith Oct. 22, 1957 2,823,822 Altman Feb. 18, 1958 2,896,416 Henry July 28, 1959 2,897,924 Fawick Aug. 4, 1959 2,930,453 McNamara Mar. 29, 1960 2,954,003 Farrell et al. Sept. 27, 1960 3,021,808 Henry Feb. 20, 1962 OTHER REFERENCES Popular Science, vol. 175, No. 4, October 1959 (pages 77-79 and 252 relied on). 

1. IN A MARINE TANKER FOR THE BULK TRANSPORT IN THE LIQUID STATE AT LOW TEMPERATURE OF ORDINARILY-GASEOUS SUBSTANCE, THE PROVISION OF AT LEAST ONE INSULATED CARGO TANK WHICH RESTS ON SUPPORTS WHICH ALLOW LATERAL EXPANSION AND CONTRACTION OF THE TANK BUT IS CONSTRAINED AGAINST LATERAL BODILY DISPLACEMENT BY A CIRCULAR SPIGOT-ANDSOCKET TYPE CONNECTION BETWEEN THE TANK AND THE SHIP''S STRUCTURAL STEEL AT THE TANK BOTTOM CENTER. 